The use of mobile communications networks has increased substantially over the two decades. Operators of the mobile communications networks have increased the number of base stations in order to meet an increased demand for service by users of the mobile communications networks. The operators of the mobile communications network need to reduce the running costs of the base station as well as improve the coverage of the base station. One option to do this is to implement systems for relaying the telecommunications signals of the mobile communication network as a distributed antenna system (DAS).
The communications standards typically provide a plurality of channels or frequency bands useable for an uplink communication from a mobile station, such as a handset, to a radio station as well as for a downlink communication from the radio station to the mobile station.
For example, the communication standard “Global System for Mobile Communications (GSM)” for mobile communications specifies different radio frequencies for use in different regions. In North America, GSM operates on the primary mobile communication bands 850 MHz and 1900 MHz. In Europe, Middle East and Asia most of the providers use the primary mobile communication bands 900 MHz and 1800 MHz. Other communications bands use other frequencies.
The constantly increasing capacity demand in wireless communications and the fact that about 80% of the traffic on the mobile distribution system is generated indoors requires new methods to provide flexible signal relaying systems to enable an efficient spectrum usage. When indoor traffic is handled with a pure outdoor macro coverage solution, the signal penetration and the signal quality is poor in the indoor environment. Indoor coverage solutions with distributed antenna systems help overcoming this issue, but the increasing capacity demand requires more advanced indoor solutions beyond pure coverage systems.
Active distributed antenna systems (DAS) or micro C-RAN have been developed to improve the coverage indoors. Theses distribution systems have the capability of dynamic traffic/cell switching of signal traffic. The radio frequency (RF) signals in the DAS are communicated between a central hub and a plurality of remote units. The central hub is connected to one or more of the base stations.
In the DAS, the coverage of a single cell is not necessarily provided by a single one of the remote units. The term “cell” is used in the present disclosure according to the definition used for GSM and is equivalent to the definition of a sector in case of UMTS and LTE standards. The cell describes a multicarrier signal provided by a base station and which is typically relayed into a sector. The plurality of the remote units relay the same telecommunication signal for the cell throughout the coverage area of the cell. In the context of this disclosure, the coverage area of the cell is defined as the sum of the individual coverage areas of the signals from each ones of the remote radio units, which are assigned to cover the cell. In case in which a plurality of antennas is connected to at least one remote radio unit, the coverage area of the cell is the sum of the individual antenna coverage areas connected to the at least one remote radio unit assigned to the cell.
The DAS may be used to provide coverage and capacity inside a building, as well as coverage and capacity in metropolitan or campus areas.
U.S. Pat. No. 7,761,093 B2 describes a method and system allowing multiple providers to share the same DAS. Each operator's base station signal is digitized and can be routed to any digital remote unit at which the signal can be digitally combined with any other signal from a different operator within the same frequency band or another frequency band supported by the remote unit. The digitally combined signals are then converted to analog RF signals in the remote unit and finally relayed into the coverage area of the remote unit.
The capacity demand in a mobile radio system is varying over time. At a same location, there are peak hours during which the highest capacity demand for signal traffic occurs and there might be times with extremely low signal traffic. The traffic demand may also very depending on the location. A mobile communications system is typically designed to cope with the expected peak hour load at each location. In other words, the mobile radio system is most of the time over-specified for the actual requirements. This results in additional power consumption.
In active DAS installations especially with low power remote units it is important to provide high linearity over the entire supported frequency band in order to support a multi-operator and multi-carrier signal transmission for any arbitrary carrier allocation within the frequency band. High linear power amplifiers are required which are typically less efficient than non-linear power amplifiers. A reduction in output power due to a reduction in or no signal traffic has a marginal influence, or even no influence, on the overall power consumption of the remote unit when using high linear power amplifiers. Power saving in such active DAS installations can be achieved by switching off one or more of the remote radio units. Switching off the remote units in their entirety can, however, result in gaps in the coverage area in the affected region at which the remote units have been switched off.
One object of the present disclosure is power savings in telecommunication distribution systems.